Method for Preparing Granular Polycrystalline Silicon Using Fluidized Bed Reactor

ABSTRACT

The present invention relates to a method for mass preparation of granular polycrystalline silicon in a fluidized bed reactor, comprising (a) a reactor tube, (b) a reactor shell encompassing the reactor tube, (c) an inner zone formed within the reactor tube, where a silicon particle bed is formed and silicon deposition occurs, and an outer zone formed in between the reactor shell and the reactor tube, which is maintained under an inert gas atmosphere, and (d) a controlling means to keep the pressure difference between the inner zone and the outer zone being maintained within the range of 0 to 1 bar, thereby capable of maintaining physical stability of the reactor tube and efficiently preparing granular polycrystalline silicon even at a relatively high reaction pressure.

TECHNICAL FIELD

The present invention relates to a method for mass production ofgranular polycrystalline silicon using a fluidized bed reactor that canbe maintained stable during a long-term operation even at a relativelyhigh pressure.

TECHNICAL PROBLEM

Generally, high-purity polycrystalline silicon is used as a basicmaterial for manufacturing semiconductor devices or solar cells. Thepolycrystalline silicon is prepared by thermal decomposition and/orhydrogen reduction of a highly-purified silicon atom-containing reactiongas, thereby allowing continuous deposition of silicon on siliconparticles.

For mass production of polycrystalline silicon, a bell-jar type reactorhas been mainly used, which provides a rod-type polycrystalline siliconproduct with a diameter of about 50-300 mm. However, the bell-jar typereactor, which consists fundamentally of the electric resistance heatingsystem, cannot be operated continuously due to inevitable limit inextending the maximum rod diameter achievable. This reactor is alsoknown to have serious problems of low deposition efficiency and highelectrical energy consumption because of limited silicon surfaces andhigh heat loss.

Alternatively, a fluidized bed reactor has recently been developed toprepare granular polycrystalline silicon with a size of 0.5-3 mm.According to this method, a fluidized bed of silicon particles is formedby the upward flow of a gas and the size of the silicon particlesincreases as the silicon atoms deposit on the particles from the siliconatom-containing reaction gas supplied to the heated fluidized bed.

As in the conventional bell-jar type reactor, the fluidized bed reactoralso uses a silane compound of Si—H—Cl system such as monosilane (SiH₄),dichlorosilane (SiH₂Cl₂), trichlorosilane (SiHCl₃), silicontetrachloride (SiCl₄) or its mixture as the silicon atom-containingreaction gas, which usually further comprises hydrogen, nitrogen, argon,helium, etc.

For the silicon deposition, the reaction temperature (i.e., temperatureof the silicon particles) should be maintained high. The temperatureshould be about 600-850° C. for monosilane, and about 900-1,100° C. fortrichlorosilane, which is most widely used.

The process of silicon deposition, which is caused by thermaldecomposition and/or hydrogen reduction of a silicon atom-containingreaction gas, includes various elementary reactions, and there arecomplex routes where silicon atoms grow into granular particlesdepending on the reaction gas. However, regardless of the kind of theelementary reaction and the reaction gas, the operation of the fluidizedbed reactor is able to provide a granular polycrystalline siliconproduct.

Here, smaller silicon particles, i.e., seed crystals become bigger insize due to continuous silicon deposition or the agglomeration ofsilicon particles, thereby losing fluidity and moving downwardseventually. The seed crystals may be prepared or generated in situ inthe fluidized bed itself, or supplied into the reactor continuously,periodically or intermittently. Thus prepared bigger particles, i.e.,polycrystalline silicon product, may be discharged from the lower partof the reactor continuously, periodically or intermittently.

Due to the relatively high surface area of the silicon particles, thefluidized bed reactor system provides a higher reaction yield than thatby the bell-jar type reactor system. Further, the granular product maybe directly used without a further processing for the following-upprocesses such as single crystal growth, crystal block or filmproduction, surface treatment and modification, preparation of chemicalmaterials for reaction or separation, or molding or pulverization ofsilicon particles. Although these follow-up processes have been operatedin a batchwise manner, the manufacture of the granular polycrystallinesilicon allows the processes to be performed in a semi-continuous orcontinuous manner.

The increase in the productivity of the fluidized bed reactor isrequired for low-cost manufacture of granular polycrystalline silicon.For this purpose, it is most effective to increase the silicondeposition rate with low specific energy consumption, which can beobtained by continuous operation of the fluidized bed reactor under highpressures. For continuous operation of the process with the fluidizedbed reactor, it is essential to secure the physical stability of thereactor components.

Unlike conventional fluidized bed reactors for preparing common chemicalproducts, serious limitations are encountered in material selection ofthe components of the fluidized bed reactor for preparingpolycrystalline silicon. Especially, considering the desired high purityof the polycrystalline silicon, the material selection of the fluidizedbed wall is important. The reactor wall is weak in physical stabilitybecause it is always in contact with silicon particles fluidizing athigh temperatures, and is subject to the irregular vibration and severeshear stress caused by the fluidized bed of the particles. However, itis very difficult to select an appropriate material among thehigh-purity non-metallic inorganic materials that are capable ofenduring a relatively high pressure condition, because a metallicmaterial is not appropriate because of high reaction temperature andchemical properties of the reaction gas. For this reason, the fluidizedbed reactor for manufacture of polycrystalline silicon inevitably has acomplex structure. It is therefore common that a reactor tube made ofquartz is positioned in an electrical resistance heater for heating thesilicon particles, and both the reactor tube and the heater aresurrounded by a metallic shell. It is preferred to fill an insulatingmaterial in between the heater and the reactor shell or outside thereactor shell to reduce heat loss.

For example, U.S. Pat. No. 5,165,908 discloses a reactor system where anelectric resistance heater encloses a reactor tube made of quartz, bothof which are protected by a jacket-shaped stainless-steel shell and aninsulating material is installed outside the shell.

U.S. Pat. No. 5,810,934 discloses a fluidized bed reactor formanufacture of polycrystalline silicon, comprising a reactor vessel,i.e., the reactor tube defining a fluidized bed; a shroud, i.e., aprotection tube surrounding the reactor tube; a heater installed outsidethe shroud; and an outer containment surrounding the heater and aninsulating material. This patent emphasizes that the protection tubemade of quartz be installed in between the reactor tube and the heaterto prevent the crack of the reactor tube and the contamination of itsinner space.

Meanwhile, the fluidized bed reactor for manufacture of polycrystallinesilicon may have a different structure depending on the heating method.

For example, U.S. Pat. No. 4,786,477 discloses a method of heatingsilicon particles with microwave penetrating through the quartz reactortube instead of applying a conventional heater outside the tube.However, this patent still has a problem of a complex structure of thereactor and fails to disclose how to increase the reaction pressureinside the quartz reactor tube.

To solve the above problem, U.S. Pat. No. 5,382,412 discloses asimple-structured fluidized bed reactor for manufacture ofpolycrystalline silicon, wherein a cylindrical reactor tube is holdvertically by a metallic reactor shell. However, this patent still hasproblems that the inner pressure cannot be increased beyond atmosphericpressure and the microwave supplying means should be combined with thereactor shell, thus failing to provide ways to overcome the mechanicalweakness of the reactor tube that is anticipated at high-pressurereaction.

TECHNICAL SOLUTION

Therefore, an object of the present invention is to provide an improvedmethod for preparing polycrystalline silicon by stable, long-termoperation of a fluidized bed reactor without being restrained byincrease in reaction pressure.

In this respect, the present inventors completed the present inventionbased on the experimental result that, if the pressure differencebetween both sides of the reactor tube is maintained within apredetermined range, the fluidized bed reactor might be operated withlong-term stability even at high pressures, satisfying variousconditions required for preparing polycrystalline silicon based on thefluidized bed process.

Another object of the present invention is to provide a method forpreparing an improved of the fluidized bed reactor which can be appliedto high-pressure operations although being composed of the materialacceptable to atmospheric-pressure operation for preparingpolycrystalline silicon.

Still another object of the present invention is to provide a method forpreparing polycrystalline silicon, which allows easy installation of aheating means for heating silicon particles to a high reactiontemperature required for preparing polycrystalline silicon.

A further object of the present invention is to provide a method forpreparing polycrystalline silicon, which may secure a long-termstability while enduring a physical stress exerted on the reactor tubeby the fluidization of silicon particles.

A still further object of the present invention is to provide a methodfor preparing polycrystalline silicon, wherein the stability of areactor may be secured despite the exposure of the reactor tube tocontinuously fluidizing silicon particles at high temperature andpressure.

The present invention also aims to provide a method which can beconveniently applied to preparing high-purity polycrystalline silicongranules while minimizing impurity contamination.

MODE FOR INVENTION

For accomplishing the aforementioned purposes, the present inventionprovides a method for preparing polycrystalline silicon using afluidized bed reactor, comprising the following procedures: (a)employing a fluidized bed reactor wherein a reactor tube is verticallyplaced within a reactor shell so as to be encompassed by the reactorshell, whereby dividing an inner space of the reactor shell into aninner zone formed within the reactor tube and an outer zone formed inbetween the reactor shell and the reactor tube, wherein a siliconparticle bed is formed and silicon deposition occurs in the inner zonewhile a silicon particle bed is not formed and silicon deposition doesnot occur in the outer zone; (b) directly or indirectly measuring and/orcontrolling an inner zone pressure using an inner pressure controllingmeans, directly or indirectly measuring and/or controlling an outer zonepressure using an outer pressure controlling means, and maintaining thedifference between the inner zone pressure and the outer zone pressurewithin 1 bar using a pressure-difference controlling means; (c)introducing a fluidizing gas into the silicon particle bed using afluidizing gas inlet means; (d) introducing a silicon atom-containingreaction gas into the silicon particle bed using a reaction gas inletmeans; (e) introducing an inert gas into the outer zone, wherebymaintaining a substantially inert gas atmosphere in the outer zone; (f)heating the silicon particle bed using a heating means installed in theinner zone and/or the outer zone; (g) discharging polycrystallinesilicon particles prepared within the inner zone to the outside of thefluidized bed reactor; (h) discharging an off-gas including a fluidizinggas that passes through the silicon particle bed, a non-reacted reactiongas and a byproduct gas to the outside of the fluidized bed reactor.

In a preferred embodiment, the reaction gas is a silicon atom-containinggas selected from the group consisting of monosilane, dichlorosilane,trichlorosilane, silicon tetrachloride and a mixture thereof.

Optionally, the reaction gas further comprises at least one gas selectedfrom the group consisting of hydrogen, nitrogen, argon, helium, hydrogenchloride and a mixture thereof.

In a preferred embodiment, the fluidizing gas is a gas selected from thegroup consisting of hydrogen, nitrogen, argon, helium, hydrogenchloride, silicon tetrachloride and a mixture thereof.

In a preferred embodiment, the inert gas comprises at least one gasselected from the group consisting of hydrogen, nitrogen, argon andhelium.

In a preferred embodiment, the outer zone pressure (Po) or the innerzone pressure (Pi) is maintained within the range of 1-15 bar.

In particular, the outer zone pressure (Po) may be controlled in therange of between maximum and minimum pressure values measurable in theinner zone.

Meanwhile, the difference between the outer zone pressure (Po) and theinner zone pressure (Pi) is maintained to satisfy the condition of 0bar≦(Pi−Po)≦1 bar, when the inner pressure controlling means isspatially connected to the inner zone through at least one meansselected from the group consisting of a fluidizing gas inlet means, areaction gas inlet means, a silicon particle outlet means and an innerzone connecting means, which are spatially connected to the siliconparticle bed.

In contrast, the difference between the outer zone pressure (Po) and theinner zone pressure (Pi) is maintained so as to satisfy the condition of0 bar≦(Po−Pi)≦1 bar, when the inner pressure controlling means isspatially connected to the inner zone through at least one meansselected from the group consisting of a gas outlet means, a silicon seedcrystals inlet means and an inner zone connecting means, which arespatially connected to an upper part of the inner zone instead of thesilicon particle bed.

In a preferred embodiment, a pressure controlling condition of thepressure-difference controlling means comprised in the inner pressurecontrolling means and/or the outer pressure controlling means isdetermined based on gas analysis of the gas that is present within ordischarged out of the inner zone and/or the outer zone by using a gasanalyzing means.

In a preferred embodiment, a packed bed of packing materials, which arenot fluidized by the flow of the fluidizing gas, is formed in a lowerpart of the silicon particle bed with the height of the packed bed beingpositioned below the outlet of the reaction gas inlet means throughwhich the reaction gas is introduced into the silicon particle bed.

Referring to the Drawings herein there is provided a detaileddescription of the present invention hereunder.

For preparing polycrystalline silicon according to the present inventionit is required to employ a fluidized bed reactor as schematically shownin FIG. 1, wherein a reactor tube is encompassed by a reactor shell sothat the space inside the reactor shell can be divided into an innerzone and an outer zone by the reactor tube. In accordance with theprimary aspect of the present invention, the pressure difference betweenthe two zones is maintained within 1 bar during the operation of thereactor.

That is, a reactor tube 2 is vertically placed within a reactor shell 1to be encompassed by the reactor shell 1, whereby dividing an innerspace of the reactor shell 1 into an inner zone 4 formed within thereactor tube 2 and an outer zone 5 formed in between the reactor shell 1and the reactor tube 2, wherein a bed of silicon particles 3, i.e., asilicon particle bed is formed and silicon deposition occurs in theinner zone while a silicon particle bed is not formed and silicondeposition does not occur in the outer zone. Then, polycrystallinesilicon is prepared according to the present invention by emptying thefluidized bed reactor and maintaining the difference between the innerzone pressure and the outer zone pressure within 1 bar.

Based on this method, granular polycrystalline silicon may be preparedby directly or indirectly measuring and/or controlling an inner zonepressure using an inner pressure controlling means, directly orindirectly measuring and/or controlling an outer zone pressure using anouter pressure controlling means, and maintaining the difference betweenthe inner zone pressure and the outer zone pressure within 1 bar bymeans of controlling pressure difference.

In addition, granular polycrystalline silicon may be prepared byintroducing a fluidizing gas into the silicon particle bed using afluidizing gas inlet means; introducing a silicon atom-containingreaction gas into the silicon particle bed using a reaction gas inletmeans; introducing an inert gas into the outer zone 5, wherebymaintaining a substantially inert gas atmosphere in the outer zone 5;discharging polycrystalline silicon particles prepared within the innerzone 4 to the outside of the fluidized bed reactor; and discharging anoff-gas including a fluidizing gas that passes through the siliconparticle bed, a non-reacted reaction gas and a byproduct gas to theoutside of the fluidized bed reactor.

First, hereunder is provided a detailed description about how toconstitute the fluidized bed reactor to be employed for the processaccording to the present invention.

FIGS. 2 and 3 are cross-sectional views of the high-pressure fluidizedbed reactor for preparing granular polycrystalline silicon, in whichsome of the embodiments according to the present invention areillustrated in a comprehensive way.

The structure of the fluidized bed reactor employed in to the presentinvention is composed of a reactor tube and a reactor shell. An innerspace of the fluidized bed reactor here is separated from an outerspace. The reactor shell 1 encompasses the reactor tube 2 that issubstantially vertically placed within the reactor shell 1. The reactortube 2 divides an inner space of the reactor shell 1 into an inner zone4 formed within the reactor tube 2 and an outer zone 5 formed in betweenthe reactor shell 1 and the reactor tube 2, wherein a silicon particlebed is formed and silicon deposition occurs in the inner zone 4 while asilicon particle bed is not formed and silicon deposition does not occurin the outer zone 5.

The reactor shell 1 is preferably made of a metallic material withreliable mechanical strength and processability such as carbon steel,stainless steel or other alloy steels. The reactor shell 1 may bedivided into a plurality of components such as 1 a, 1 b, 1 c and 1 d asset forth in FIGS. 2 and 3 for convenience in fabrication, assembly anddisassembly.

It is important to assemble the components of the reactor shell 1 byusing gaskets or sealing materials for complete sealing. The componentsmay have various structures of a cylindrical pipe, a flange, a tube withfittings, a plate, a cone, an ellipsoid and a double-wall jacket with acooling medium flowing in between the walls. The inner surface of eachcomponent may be coated with a protective layer or be installed with aprotective tube or wall, which may be made of a metallic material or anon-metallic material such as organic polymer, ceramic and quartz.

Some of the components of the reactor shell 1, illustrated as 1 a, 1 b,1 c and 1 d in FIGS. 2 and 3, are preferably maintained below a certaintemperature by using a cooling medium such as water, an oil, a gas andair for protecting the equipment or operators, or for preventing anythermal expansion in equipment or a safety accident. Although not setforth in FIGS. 2 and 3, the components that need to be cooled maypreferably be equipped with a coolant-circulating means at their inneror outer walls. Instead of cooling, the reactor shell 1 may comprise aninsulating material on the outer wall.

The reactor tube 2 may be of any shape only if it can be hold by thereactor shell 1 in such a manner that it can separate the inner space ofthe reactor shell 1 into an inner zone 4 and an outer zone 5. Thereactor tube 2 may be of a structure of a simple straight tube as inFIG. 2, a shaped tube as in FIG. 3, a cone or an ellipsoid, and eitherone end or both ends of the reactor tube 2 may be formed into a flangeshape. Further, the reactor tube 2 may comprise a plurality ofcomponents and some of these components may be installed in the form ofa liner on the inner wall of the reactor shell 1.

The reactor tube 2 is preferred to be made of an inorganic material,which is stable at a relatively high temperature, such as quartz,silica, silicon nitride, boron nitride, silicon carbide, graphite,silicon, glassy carbon or their combination.

Meanwhile, a carbon-containing material such as silicon carbide,graphite, glassy carbon may generate carbon impurity and contaminate thepolycrystalline silicon particles. Thus, if the reactor tube 2 is madeof a carbon-containing material, the inner wall of the reactor tube 2 ispreferred to be coated or lined with materials such as silicon, silica,quartz or silicon nitride. Then, the reactor tube 2 may be structured ina multi-layered form. Therefore, the reactor tube 2 is of one-layered ormultilayered structure in the thickness direction, each layer of whichis made of a different material.

Sealing means 41 a, 41 b may be used for the reactor shell 1 to safelyhold the reactor tube 2. The sealing means are preferred to be stable ata temperature of above 200° C. and may be selected from organic polymer,graphite, silica, ceramic, metal or their combination. However,considering the vibration and thermal expansion during reactoroperation, the sealing means 41 a, 41 b may be installed less firmly tolower the possibility of cracking of the reactor tube 2 in the course ofassembly, operation and disassembly.

The partition of the inner space of the reactor shell 1 by the reactortube 2 may prevent the silicon particles in the inner zone 4 fromleaking into the outer zone 5 and differentiate the function andcondition between the inner zone 4 and the outer zone 5.

In addition to the process for preparing granular polycrystallinesilicon according to present invention as described above, it isrequired for carrying out a high-temperature silicon deposition reactionto heat silicon particles in the silicon bed by a heating meansinstalled in the inner zone 4 and/or the outer zone 5. One or aplurality of heating means 8 a, 8 b may be installed in the inner zone 4and/or the outer zone 5 in various manner. For example, a heating meansmay be installed only in the inner zone 4 or in the outer zone 5 asillustrated in FIG. 2 in a comprehensive manner. Meanwhile, a pluralityof heating means may be installed in both zones, or only in the outerzone 5 as illustrated in FIG. 3. Besides, although it is not illustratedin Drawings, a plurality of heating means 8 a, 8 b may be installed onlyin the inner zone 4. Otherwise, a single heating means may be installedin the outer zone 5 only.

The electric energy is supplied to the heating means 8 a, 8 b through anelectric energy supplying means 9 a-9 f installed on or through thereactor shell 1. The electric energy supplying means 9 a-9 f, whichconnects the heating means 8 a, 8 b in the reactor and an electricsource E outside the reactor, may comprise a conductive metalliccomponent in the form of a cable, a bar, a rod, a shaped body, a socketor a coupler. Otherwise the electric energy supplying means 9 a-9 f maycomprise an electrode that is made of a material such as graphite,ceramic (e.g., silicon carbide), metal or a mixture thereof, and isfabricated in various shapes for connecting the electric source E withthe heating means. Alternatively, the electric energy supplying meanscan be prepared by extending a part of the heating means 8 a, 8 b. Incombining the electric energy supplying means 9 a-9 f with the reactorshell 1, electrical insulation is also important besides the mechanicalsealing for preventing gas leak. Further, it is desirable to cool downthe temperature of the electric energy supplying means 9 by using acirculating cooling medium such as water, an oil and a gas.

Meanwhile, a gas inlet means should be installed at the fluidized bedreactor to form a fluidized bed, where silicon particles can move by gasflow, within the reactor tube 2, i.e., in a lower part of the inner zone4, for preparation of polycrystalline silicon by the silicon depositionon the surface of the fluidizing silicon particles.

The gas inlet means comprises a fluidizing gas inlet means 14, 14′ forintroducing a fluidizing gas 10 into the silicon particle bed and areaction gas inlet means 15 for introducing a silicon atom-containingreaction gas the silicon particle bed, both of which are installed incombination with the reactor shell 1 b.

In this respect, granular polycrystalline silicon may be preparedaccording to the present invention by introducing a fluidizing gas 10into the silicon particle bed using a fluidizing gas inlet means 14,14′, and introducing a silicon atom-containing reaction gas 11 into thesilicon particle bed using a reaction gas inlet means 15.

As used herein, “a fluidizing gas” 10 refers to a gas introduced tocause some or most of the silicon particles 3 to be fluidized in thefluidized bed formed within the inner zone 4. In the present invention,hydrogen, nitrogen, argon, helium, hydrogen chloride (HCl), silicontetrachloride (SiCl₄) or a mixture thereof may be used as the fluidizinggas 10.

As used herein, “a reaction gas” 11 refers to a source gas containingsilicon atoms, which is used to prepare the polycrystalline siliconparticles. In the present invention, monosilane (SiH₄), dichlorosilane(SiH₂Cl₂), trichlorosilane (SiHCl₃), silicon tetrachloride (SiCl₄) or amixture thereof may be used as the silicon-containing reaction gas 11.The reaction gas 11 may further comprise at least one gas selected fromhydrogen, nitrogen, argon, helium and hydrogen chloride. Further, inaddition to serving as a source for silicon deposition, the reaction gas11 contributes to the fluidization of the silicon particles 3 as thefluidizing gas 10 does.

The fluidizing gas inlet means 14, 14′ and the reaction gas inlet means15 may comprise a tube or nozzle, a chamber, a flange, a fitting, agasket, etc, respectively. Among these components, the parts exposed tothe inner space of the reactor shell 1, especially to the lower part ofthe inner zone 4, where the parts are likely to contact the siliconparticles 3, are preferred to be made of a tube, a liner or a shapedarticle the material of which is selected from those applicable to thereactor tube 2.

Optionally, the lower part of the fluidized bed 4 a in the inner zone 4may comprise an additional gas distributing means 19 for distributingthe fluidizing gas 10 in combination with the fluidizing gas inlet means14, 14′ and the reaction gas inlet means 15. The gas distributing means19 may have any geometry or structure including a multi-hole or porousdistribution plate, a packed bed of packing materials submerged in theparticle bed, a nozzle or a combination thereof. When the gasdistributing means 19 is additionally employed, its component, like theupper surface of the gas distributing means 19, which is likely tocontact the silicon particles 3, is preferably made of an inorganicmaterial that can be used for the reactor tube 2. To prevent silicondeposition on the upper surface of the gas distributing means 19, theoutlet of the reaction gas inlet means 15, through which a reaction gas11 is injected into the interior of the fluidized bed, is preferablypositioned higher than the upper part of the gas distributing means 19.

In the reactor inner zone 4, the fluidizing gas 10, which is required toform the fluidized bed 4 a of silicon particles, may be supplied invarious ways depending on how the fluidizing gas inlet means 14, 14′ isconstituted. For example, as illustrated in FIG. 2, the fluidizing gas10 may be supplied by a fluidizing gas inlet means 14, 14′ coupled withthe reactor shell 1 so that a gas chamber may be formed in lower part ofthe distribution plate-shaped gas distributing means 19. Alternatively,as illustrated in FIG. 3, a fluidizing gas 10 may be supplied by afluidizing gas inlet means 14 coupled with the reactor shell 1 so thatone or a plurality of fluidizing gas nozzle outlet may be positioned inbetween the gas distributing means 19 that comprises a third packed bedof packing materials other than those fluidizing silicon particles.Meanwhile, the gas distributing means 19 and the fluidizing gas inletmeans 14, 14′ may be constituted by using both the distribution plateand the packing materials.

As an example, in addition to the distribution plate and/or thenozzle(s) for introducing the fluidizing gas 10, it is possible toemploy a packed bed of packing materials other than the siliconparticles 3 to be included in the silicon product particles 3 b. Thepacking materials may have a sufficient size or mass, so as not to befluidized by the flow of the fluidizing gas 10, and may be shaped like asphere, an ellipsoid, a pellet, a nugget, a tube, a rod, or a ring, etc.The packing materials composition may be selected from those applicableto the reactor tube 2 as well as high-purity silicon, with their averagesize being within the range of 5-50 mm.

When employed as a gas distributing means 19, the packed bed of packingmaterials, which are not fluidized by the flow of the fluidizing gas 10,may preferably be formed in a lower part of the silicon particle bedwith the height of the packed bed being positioned below the outlet ofthe reaction gas inlet means 15 through which the reaction gas 11 isintroduced into the silicon particle bed. In this case, the movement ofsilicon particles and the flow of the fluidizing gas may occur in thespace formed between the packing materials, while the heat transferreddownward from the fluidized bed of silicon particles 3 heated by theheating means being utilized for preheating the upcoming fluidizing gas10.

In the present invention, the polycrystalline silicon particles areprepared in the inner zone 4 of the reactor based on the silicondeposition. Following the supply of the reaction gas 11 through thereaction gas inlet means 15, the silicon deposition occurs on thesurface of the silicon particles 3 heated by the heating means 8 a, 8 b.

In addition, granular polycrystalline silicon may be prepared bydischarging 11 polycrystalline silicon particles prepared within theinner zone 4 to the outside of the fluidized bed reactor.

A particle outlet means 16 is also required to be combined with thereactor shell 1 to discharge thus prepared silicon particles from theinner zone 4 to the outside of the fluidized bed reactor.

An outlet pipe, which constitutes the particle outlet means 16, may beassembled with the reaction gas inlet means 15 as illustrated in FIG. 2.Alternatively, it may be installed independently of the reaction gasinlet means 15 as illustrated in FIG. 3. Through the particle outletmeans 16 the silicon particles 3 b may be discharged when required fromthe fluidized bed 4 a in a continuous, periodic, or intermittent way.

As illustrated in FIG. 2, an additional zone may be combined with thereactor shell 1. The additional zone can be provided at some part or alower part of the fluidizing gas inlet means 14′, allowing a space forthe silicon particles 3 b to reside or stay with an opportunity ofcooling before being discharged from the reactor.

Silicon particles 3, i.e., silicon particles 3 discharged from the innerzone 4 to the outside of the reactor according to the present invention,may be delivered to a storage member or a transfer member of thepolycrystalline silicon product, which is directly connected to thereactor. Meanwhile, thus-prepared silicon product particles 3 b may havea particle-size distribution due to nature of the fluidized bed reactor,and smaller particles included therein may be used as seed crystals 3 afor the silicon deposition. It is thus possible that the silicon productparticles 3 b discharged from the inner zone 4 to the outside of thereactor may be delivered to a particle separation member where theparticles can be separated by size. Then the larger particles may bedelivered to the storage member or the transfer member, while thesmaller particles are used as seed crystals 3 a.

Otherwise, considering the relatively high-temperature of the siliconparticle bed 4 a within the inner zone 4, the silicon particles 3 b arepreferred to be cooled down while being discharged through the particleoutlet means 16. For this purpose, a cooling gas such as hydrogen,nitrogen, argon, helium, or a mixture thereof may flow in the particleoutlet means 16, or a cooling medium such as water, oil or gas may becirculated through the wall of the particle outlet means 16.

Alternatively, although it is not illustrated in Drawings, the particleoutlet means 16 may be constituted in combination with the inner spaceof the reactor shell 1 (e.g. 14′ in FIG. 2) or a lower part of thereactor shell (e.g., 1 b in FIGS. 2 and 3), allowing a sufficient spacefor the silicon particles 3 b to reside or stay with an opportunity ofcooling for a certain period of time before being discharged to theoutside of the reactor.

It is necessary to prevent the silicon product particles 3 b from beingcontaminated while discharged from the reactor through the particleoutlet means 16. Therefore, in constituting the particle outlet means16, the elements that may contact high-temperature silicon productparticles 3 b may be made of a tube, a liner or a shaped product that ismade of or coated with an inorganic material applicable to the reactortube 2. These elements of the particle outlet means 16 are preferred tobe coupled to the metallic reactor shell and/or a protection pipe.

The components of the particle outlet means 16, which are in contactwith the relatively low-temperature product particles or comprise acooling means on their wall, may be made of a metal-material tube, aliner or a shaped product, the inner wall of which is coated or linedwith a fluorine-containing polymer material.

As mentioned above, the silicon product particles 3 b may be dischargedfrom the inner zone 4 in the reactor through the particle outlet means16 to a storage member or a transfer member of the polycrystallinesilicon product in a continuous, periodic, or intermittent way.

Meanwhile, a particle separation member may be installed in between thereactor and the product storage member, to separate the silicon productparticles 3 b by size and use small-sized particles as seed crystals 3a. Various commercial devices may be used as the particle separationmember in the present invention.

It is desirable to constitute the elements of the particle separationmember, which may be in contact with the silicon product particles 3 b,by using the same material as the one used in the particle outlet means16, or pure polymer material that does not contain either an additive ora filler.

For continuous operation of the fluidized bed reactor, it is necessaryto combine the reactor shell 1 d with a gas outlet means 17 which isinstalled for discharging an off-gas from the fluidized bed reactor. Theoff-gas 13 comprises a fluidizing gas that passes through the siliconparticle bed, a non-reacted reaction gas and a byproduct gas, passesthrough the upper part of the inner zone, 4 c, and is finally dischargedto the outside of the fluidized bed reactor.

Fine silicon particles or high-molecular-weight byproducts entrained inthe off-gas 13 may be separated from an additional off-gas treatingmeans 34.

As illustrated in FIGS. 2 and 3, an off-gas treating means 34, whichcomprises a cyclone, a filter, a packed column, a scrubber or acentrifuge, may be installed outside the reactor shell 1 or at the upperzone 4 c of the inner zone within the reactor shell 1.

Fine silicon particles, thus separated from the off-gas treating means34, may be used for another purpose, or as seed crystals 3 a forpreparing silicon particles after being recycled into the fluidized bed4 a at the inner zone of the reactor.

When manufacturing silicon particles in a continuous manner, it ispreferred to maintain the number and the average particle size of thesilicon particles, which forms the fluidized bed 4 a, within a certainrange. This may be obtained by supplementing nearly the same number ofthe seed crystals within the fluidized bed 4 a as that of the dischargedsilicon product particles 3 b.

As mentioned above, the fine silicon particles or powders separated fromthe off-gas treating means 34 may be recycled as seed crystals, buttheir amount can not be sufficient. It is then required to furtheryield, generate or prepare additional silicon seed crystals forcontinuous preparation of the silicon particles as required in thefluidized bed.

In this regard, it may be necessary to further separate the smallersilicon particles among the silicon product particles 3 b and use themas seed crystals 3 a. However, the additional process for separatingseed crystals 3 a from the product particles 3 b outside the fluidizedbed reactor has drawbacks of high chances of contamination anddifficulties in operation.

Instead of the additional separation of product particles 3 b, it isalso possible to separate smaller particles out of them and to recyclethe smaller particles as seed crystals into the fluidized bed. To thispurpose an additional particle separation member may be installed in themiddle of a discharge path included in the particle outlet means 16.Supplying a gas into the pathway in a counter-current manner leads tocooling of the product particles 3 b, separation of smaller particlesout of them and recycling of the smaller particles into the fluidizedbed 4 a. This reduces the burden of preparing or supplying seedcrystals, and increases the average particle size of the final siliconproduct particles 3 b while decreasing their particle size distribution.

As another embodiment, the silicon seed crystals may be prepared bypulverizing some of silicon product particles 3 b discharged through theparticle outlet means 16 into seed crystals in a separate pulverizingapparatus. Thus prepared seed crystals 3 a may be introduced into theinner zone 4 of the reactor in a continuous, periodic or intermittentlyway as required. One example when seed crystals 3 a is downwardlyintroduced into the inner zone 4 is illustrated in FIG. 2, where a seedcrystals inlet means 18 is combined with the topside of the reactorshell 1 d. This method allows an efficient control in the average sizeand the feeding rate of seed crystals 3 a as required, while it has adrawback of requiring an additional pulverizing apparatus.

On the contrary, silicon particles may be pulverized into seed crystalsinside fluidized bed 4 a by using an outlet nozzle of a reaction gasinlet means 15 combined with the reactor shell or an additionallyinstalled gas nozzle for a high-speed gas jet inside the fluidized bedallowing particle pulverization. This method has an economic advantagebecause it needs no additional pulverizing device, while having adrawback that it is difficult to control the size and the amount of theseed crystals being generated in the reactor within a predeterminedacceptable range.

In the present invention, the inner zone 4 comprises all spaces requiredfor forming a silicon particle bed 4 a, introducing a fluidizing gas 10and a reaction gas 11 into the silicon particle bed 4 a, allowingsilicon deposition, and discharging the off-gas 13 containing afluidizing gas, a non-reacted reaction gas and a byproduct gas.Therefore, the inner zone 4 plays a fundamental role for silicondeposition in the fluidized bed of silicon particles 3 and preparationof polycrystalline silicon product particles.

In contrast to the inner zone 4, the outer zone 5 is an independentlyformed space in between the outer wall of the reactor tube 2 and thereactor shell 1, where a silicon particle bed 3 is not formed andsilicon deposition does not occur because the reaction gas is notsupplied therein. Therefore, the outer zone 5 may be defined as theinner space within the reactor shell 1 excluding the inner zone or thespace formed in between the reactor shell 1 and the reactor tube 2.

In addition to the above-mentioned embodiments according to the presentinvention, granular polycrystalline silicon may be prepared byintroducing an inert gas into the outer zone 5, whereby maintaining asubstantially inert gas atmosphere in the outer zone 5.

The importance and roles of the outer zone 5 maintained in an inert gasatmosphere according to the present invention may be summarized asfollows.

First, the outer zone 5 provides a space for protecting the reactor tube2 by maintaining pressure difference between the inner zone 4 and theouter zone 5 within a certain range.

Second, the outer zone 5 provides a space for installing an insulatingmaterial 6 that prevents or decreases heat loss from the reactor.

Third, the outer zone 5 provides a space for a heater to be installedaround the reactor tube 2.

Fourth, the outer zone 5 provides a space for maintaining asubstantially inert gas atmosphere outside the reactor tube 2 to preventdangerous gas containing oxygen and impurities from being introducedinto the inner zone 4, and for safely installing and maintaining thereactor tube 2 inside the reactor shell 1.

Fifth, the outer zone 5 allows a real-time monitoring of the status ofthe reactor tube 2 during operation. The analysis or measurement of theouter-zone gas sample from the outer zone connecting means 28 may revealthe presence or concentration of a gas component that may exist in theinner zone 4, the change of which may indirectly reveal an accident atthe reactor tube.

Sixth, the outer zone 5 provides a space for installing a heater 8 bsurrounding the reactor tube 2, as illustrated in FIG. 3, for heating upand chemically removing the silicon deposit layer accumulated on theinner wall of the reactor tube 2 due to silicon deposition operation.

Lastly, the outer zone 5 provides a space required for efficientassembly or disassembly of the reactor tube 2 and the inner zone 4.

According to the present invention, the outer zone 5 plays manyimportant roles as mentioned above. Thus, the outer zone may bepartitioned into several sections in an up-and-down and/or a radial orcircumferential direction, utilizing one or more of tubes, plates,shaped articles or fittings as partitioning means.

When the outer zone 5 is further partitioned according to the presentinvention, the divided sections are preferred to be spatiallycommunicated with each other while having substantially the sameatmospheric condition and pressure.

An insulating material 6, which may be installed in the outer zone 5 forgreatly reducing heat transfer via radiation or conduction, may beselected from industrially acceptable inorganic materials in the form ofa cylinder, a block, fabric, a blanket, a felt, a foamed product, or apacking filler material.

The heating means 8 a, 8 b, connected to an electric energy supplyingmeans 9, which is connected to the reactor shell for maintainingreaction temperature in the fluidized bed reactor, may be installed inthe outer zone 5 only, or installed alone within the inner zone 4,especially within the silicon particle bed 4 a. The heating means 8 a, 8b, may be installed in both the inner zone 4 and the outer zone 5, ifrequired, as illustrated in FIG. 2. FIG. 3 illustrates an example when aplurality of independent heating means 8 a, 8 b are installed in theouter zone 5.

When a plurality of heating means 8 a, 8 b are installed in thefluidized bed reactor, they may be electrically connected in series orparallel relative to an electric source E. Alternatively, the powersupplying system comprising an electric source E and an electric energysupplying means 9 a-9 f may be constituted independently as illustratedin FIGS. 2 and 3.

As illustrated in FIG. 2, the heater 8 a installed within the siliconparticle bed 4 a may have an advantage of directly heating siliconparticles in the fluidized bed. In this case, to prevent accumulativesilicon deposition on the surface of the heater 8 a, the heater 8 a ispreferably positioned lower than the reaction gas outlet of a reactiongas inlet means 15.

In the present invention, an inert gas connecting means 26 a, 26 b isinstalled on the reactor shell, independently of the inner zone 4, tomaintain a substantially inert gas atmosphere in the outer zone 5precluding silicon deposition. The inert gas 12 may be one or moreselected from hydrogen, nitrogen, argon and helium.

An inert gas connecting means 26 a, 26 b, which is installed on orthrough the reactor shell and spatially connected to the outer zone 5,has the function of piping connection for supplying or discharging aninert gas 12, and may be selected from a tube, a nozzle, a flange, avalve, a fitting or a combination thereof.

Meanwhile, apart from the inert gas connecting means 26 a, 26 b, areactor shell, which is spatially exposed to the outer zone 5 directlyor indirectly, may be equipped with an outer zone connecting means 28.Then, the outer zone connecting means 28 may be used to measure and/orcontrol temperature, pressure or gas component. Although even a singleinert gas connecting means 26 a, 26 b may allow to maintain asubstantially inert gas atmosphere in the outer zone 5, the supply ordischarge of an inert gas may be independently performed by using adouble-pipe or a plurality of inert gas connecting means 26 a, 26 b.

Further, the inert gas connecting means 26 a, 26 b maintains anindependent inert gas atmosphere in the outer zone 5, and may also beused for measuring and/or controlling flow rate, temperature, pressureor gas component, which can also be performed by using the outer zoneconnecting means 28.

FIGS. 2 and 3 provide various examples in a comprehensive way where theouter zone pressure (Po), i.e., pressure in the outer zone 5 is measuredand/or controlled by using the inert gas connecting means 26 a, 26 b orouter zone connecting means 28.

The outer zone connecting means 28 may be installed to measure and/orcontrol the maintenance of the outer zone 5, independently of or onbehalf of the inert gas connecting means 26 a, 26 b. The outer zoneconnecting means 28 has the function of piping connection, and may beselected from a tube, a nozzle, a flange, a valve, a fitting or theircombination. If the inert gas connecting means 26 a, 26 b is notinstalled, the outer zone connecting means 28 may be used to supply ordischarge an inert gas 12 as well as to measure or control temperature,pressure or gas component. Therefore, it is not necessary todifferentiate the inert gas connecting means 26 a, 26 b from the outerzone connecting means 28 in respect of shape and function.

Meanwhile, unlike the outer zone 5 where pressure may be maintainednearly constant irrespective of position and time, there existsinevitably a pressure difference within the inner zone 4 according tothe height of the fluidized bed 4 a of silicon particles 3. Thus, theinner zone pressure (Pi), i.e., pressure in the inner zone 4 changesaccording to the height in the inner zone 4.

Although the pressure drop imposed by the fluidized bed of solidparticles depends on the height of the fluidized bed, it is common tomaintain the pressure drop by fluidized bed less than about 0.5-1 barunless the height of the fluidized bed is excessively high. Further,irregular fluctuation of the pressure is inevitable with time due to thenature of the fluidization of solid particles. Thus, pressure may varyin the inner zone 4 according to position and time.

Considering these natures, the pressure controlling means for the innerzone pressure (Pi), i.e., the inner pressure controlling means 30 fordirectly or indirectly measuring and/or controlling pressure in theinner zone 4 may be installed at such a point among various positionsthat it may be spatially connected to the inner zone 4.

Pressure controlling means according to the present invention, i.e., theinner pressure controlling means 30 and the outer pressure controllingmeans 31 may be installed on or through various positions depending onthe details of the reactor assembly as well as on the operationalparameters to be controlled.

The inner pressure controlling means 30 may be spatially connected tothe inner zone 4 through an inner zone connecting means 24, 25, afluidizing gas inlet means 14, a reaction gas inlet means 15, a particleoutlet means 16, or a gas outlet means 17, which are spatially exposeddirectly or indirectly to the inner zone 4.

Meanwhile, the pressure controlling means for the outer zone pressure(Po), i.e., the outer pressure controlling means 31 may be spatiallyconnected to the outer zone 5 through an outer zone connecting means 28or an inert gas connecting means 26 a, 26 b, etc., which are installedon or through the reactor shell 1 and spatially exposed directly orindirectly to the outer zone 5.

According to a preferable embodiment of the present invention forpreparing granular polycrystalline silicon, the inner pressurecontrolling means 30 and/or the outer pressure controlling means 31comprise the components necessary for directly or indirectly measuringand/or controlling pressure.

Either of the pressure controlling means, 30 and 31, comprises at leastone selected from the group consisting of: (a) a connecting pipe orfitting for spatial connection; (b) a manually-operated, semi-automatic,or automatic valve; (c) a digital- or analog-type pressure gauge orpressure-difference gauge; (d) a pressure indicator or recorder; and (e)an element constituting a controller with a signal converter or anarithmetic processor.

The inner pressure controlling means 30 is interconnected with the outerpressure controlling means 31 in the form of a mechanical assembly or asignal circuit. Further, either of the pressure controlling means may bepartially or completely integrated with a control system selected fromthe group consisting of a central control system, a distributed controlsystem and a local control system.

Although the inner pressure controlling means 30 and/or the outerpressure controlling means 31 may be independently constituted in termsof pressure, either of the pressure controlling means may be partiallyor completely integrated with a means for measuring and/or controlling aparameter selected from the group consisting of flow rate, temperature,gas component and particle concentration, etc.

Meanwhile, either of the controlling means, 30 or 31, may furthercomprise a separation device such as a filter or a scrubber forseparating particles, or a container for buffering pressure. Thisprotects the component of the pressure controlling means fromcontamination by impurities, and also provides a means to bufferpressure changes.

As an example, the inner pressure controlling means 30 may be installedat or connected to the inner zone connecting means 24, 25, which isinstalled on or through the reactor shell and is spatially exposeddirectly or indirectly to an inner zone 4 for measurement of pressure,temperature or gas component or for viewing inside the reactor. Byconstituting the inner pressure controlling means 30 so that it may beconnected to the inner zone connecting means 24, 25, pressure in anupper part of the inner zone 4 c may be stably measured and/orcontrolled although it is difficult to detect the time-dependentpressure fluctuation due to the fluidized bed of silicon particles. Formore accurate detection of the time-dependent pressure fluctuationrelated with the fluidized bed, the inner zone connecting means may beinstalled so that it may be spatially connected to the inside of thefluidized bed.

The inner pressure controlling means 30 may also be installed at orconnected to other appropriate positions, i.e., a fluidizing gas inletmeans 14 or a reaction gas inlet means 15 or a particle outlet means 16or a gas outlet means 17, etc., all of which are combined with thereactor shell thus being spatially connected to the inner zone 4.

Further, a plurality of inner pressure controlling means 30 may beinstalled at two or more appropriate positions which ultimately allowspatial connection with the inner zone 4 through the inner zoneconnecting means 24, 25 and/or those at other positions.

As mentioned above, the presence of silicon particles affects the innerzone pressure, Pi. Thus, the measured value of Pi varies according tothe position where the inner pressure controlling means 30 is installed.Following observations by the present inventors, the value of Pi isinfluenced by the characteristics of the fluidized bed and by thestructure of a fluidizing gas inlet means 14 or a reaction gas inletmeans 15 or a particle outlet means 16 or a gas outlet means 17, but itspositional deviation according to pressure measurement point is normallyobserved to be not greater than 1 bar.

Then, the present invention permits to carry out directly or indirectlymeasuring and/or controlling an inner zone pressure using the innerpressure controlling means 30, directly or indirectly measuring and/orcontrolling an outer zone pressure using an outer pressure controllingmeans 31, and maintaining the difference between the inner zone pressureand the outer zone pressure within 1 bar using the pressure-differencecontrolling means.

In a preferred embodiment, the outer pressure controlling means 31, fordirectly or indirectly measuring and/or controlling the outer zonepressure, i.e., pressure in the outer zone 5, is preferred to beinstalled so that it may be spatially connected to the outer zone 5. Theposition where the outer pressure controlling means 31 may be connectedor installed includes, for example, an outer zone connecting means 28 oran inert gas connecting means 26 a, 26 b installed on or through thereactor shell, which is spatially connected to the outer zone 5 directlyor indirectly. In the present invention, the outer zone 5 is required tobe maintained in a substantially inert gas atmosphere. Thus, the outerzone connecting means 28 may also comprise the function of an inert gasconnecting means 26 a that may be used for introducing an inert gas 12to the outer zone 5 or an inert gas connecting means 26 b that may beused for discharging an inert gas 12 from the outer zone 5. This meansthat the inert gas inlet means 26 a or the inert gas outlet means 26 bmay be used as the inert gas connecting means 26 and the outer zoneconnecting means 28. Further, the inert gas inlet means 26 a and theinert gas outlet means 26 b may be installed separately at thoseconnecting means 26, 28, or be connected to either of those connectingmeans 26, 28 as an integrated double tube-type structure. Therefore, itis possible to spatially connect the outer zone 5 to the outer pressurecontrolling means 31 for directly or indirectly measuring and/orcontrolling pressure in the outer zone 5 through an inert gas connectingmeans 26 a, 26 b or an outer zone connecting means 28.

In the present invention, the inner pressure controlling means 30 and/orthe outer pressure controlling means 31 may be used to maintain thevalue of |Po−Pi|, i.e. the difference between the pressure in the innerzone 4, i.e., the inner zone pressure (Pi) and the pressure in the outerzone 5, i.e., the outer zone pressure (Po) within 1 bar. However, itshould be noted in constituting the inner pressure controlling means 30that Pi may vary depending on the position selected for connection tothe inner zone.

The value of Pi measured through an inner zone connecting means 24, 25,a fluidizing gas inlet means 14, a reaction gas inlet means 15, or aparticle outlet means 16, etc., which are installed at the positionsspatially connected to an inner or lower part of the fluidized bed, ishigher than the value of Pi measured through an inner zone connectingmeans, a gas outlet means 17 or silicon seed crystals inlet means 18,etc., which are installed at the positions spatially connected to aspace like an upper part of the inner zone 4 c and are not in directcontact with the fluidized bed of silicon particles.

Especially, the pressure value, measured through an inner zoneconnecting means, a fluidizing gas inlet means 14 or a particle outletmeans 16, which is spatially connected to a lower part of the fluidizedbed of silicon particles, shows a maximum inner zone pressure value,Pi_(max). On the contrary, a minimum inner zone pressure value,Pi_(min), may be obtained when measured through a gas outlet means 17 oran inner zone connecting means 24, 25, which is not in direct contactwith the fluidized bed. This is because there is a pressure differencedepending on the height of the fluidized bed of silicon particles 4 aand the value of Pi is always higher in the lower part as compared tothat in the upper part of the fluidized bed.

This pressure difference increases with the height of the fluidized bed.An excessively high bed with the pressure difference being 1 bar orhigher is not preferred because the height of the reactor becomes toohigh to be used. In contrast, a very shallow bed with the pressuredifference of 0.01 bar or lower is not preferred either, because theheight and volume of the fluidized bed is too small to achieve anacceptable minimum productivity of the reactor.

Therefore, the pressure difference in the fluidized bed is preferred tobe within the range of 0.01-1 bar. That is, pressure differences betweenmaximum pressure value (Pi_(max)) and minimum pressure value (Pi_(min))in the inner zone 4 is preferred to be within 1 bar.

When maintaining the value of |Po−Pi|, i.e., pressure difference betweeninside and outside the reactor tube 2 within the range of 0 to 1 bar, itshould be noted that the pressure difference may vary depending on theheight of the reactor tube 2.

It is preferred to meet the requirements of Po≦Pi and 0 bar≦(Pi−Po)≦1bar, when the inner pressure controlling means 30 is spatially connectedto the inner zone 4 through an inner zone connecting means, a fluidizinggas inlet means 14, a reaction gas inlet means 15 or a particle outletmeans 16, etc., which is connected to an inner or lower part of thefluidized bed of silicon particles, the pressure of which is higher thanthat of the upper part of the inner zone 4 c.

In contrast, it is preferred to meet the requirements of Pi≦Po and 0bar≦(Po−Pi)≦1 bar, when the inner pressure controlling means 30 isspatially connected to the inner zone 4 through a gas outlet means 17, asilicon seed crystals inlet means 18, or an inner zone connecting means24, 25, etc., which is not spatially connected to the silicon particlebed but connected to an upper part of the inner zone 4 c, the pressureof which is lower than that of the inner or lower part of the fluidizedbed.

It may also be permissible to constitute the inner pressure controllingmeans 30 and/or the outer pressure controlling means 31 in such mannerthat Pi or Po is represented by an average of a plurality of pressurevalues measured at one or more positions. Especially, because there maybe pressure difference in the inner zone 4 depending on the connectionposition, the inner pressure controlling means 30 may comprise acontrolling means with an arithmetic processor that is capable ofestimating an average value of pressure from those values measured withtwo or more pressure gauges.

Therefore, when maintaining the value of |Po−Pi|, i.e., the pressuredifference value between inside and outside the reaction tube, within 1bar, it is preferred to maintain the pressure value at outer zone 5, Po,in between Pi_(max) and Pi_(min), which are maximum and minimum values,respectively, that can be measured by the spatial connection of thosepressure controlling means to the inner zone 4.

The inner pressure controlling means 30 and/or outer pressurecontrolling means 31 according to the present invention should comprisea pressure-difference controlling means that maintains the value of|Po−Pi| within 1 bar.

The pressure-difference controlling means may be comprised in only oneof the inner pressure controlling means 30 or the outer pressurecontrolling means 31, or in both of the controlling means independently,or in the two controlling means 30, 31 in common.

However, it is preferred to apply and maintain a pressure-differencecontrolling means with consideration that pressure value variesdepending on the position selected for measuring the pressure in theinner zone 4, Pi. When Pi is measured through a fluidizing gas inletmeans 14, a reaction gas inlet means 15, a particle outlet means 16, oran inner zone connecting means, etc., which are spatially connected toinner part of the fluidized bed, especially to the lower part of thefluidized bed, where the pressure is higher than that in an upper partof the inner zone 4 c, the pressure-difference controlling means maypreferably be operated so that the requirements of Po≦Pi and 0bar≦(Pi−Po)≦1 are satisfied. Then, the pressure-difference controllingmeans enables the outer zone pressure (Po) and inner zone pressure (Pi)to satisfy the requirement of 0 bar≦(Pi−Po)≦1 bar, with the innerpressure controlling means 30 being spatially connected to an inner partof the fluidized bed through a fluidizing gas inlet means 14 or areaction gas inlet means 15 or a particle outlet means 16 or an innerzone connecting means.

In contrast, it is preferred to apply and maintain a pressure-differencecontrolling means so that the requirements of Pi≦Po and 0 bar≦(Po−Pi)≦1bar may be satisfied if Pi is measured at a position that is spatiallyconnected to the upper part of the inner zone 4 c among various parts ofthe inner zone 4. Then, the pressure-difference controlling meansenables the requirement of 0 bar≦(Po−Pi)≦1 bar to be satisfied, with theinner pressure controlling means 30 being spatially connected to theinner zone 4 through a gas outlet means 17, a silicon seed crystalsinlet means 18, or an inner zone connecting means 24, 25, which are notin direct contact with the fluidized bed of silicon particles.

In the present invention, being comprised in only one of the innerpressure controlling means 30 or the outer pressure controlling means31, in both of the two controlling means 30, 31 independently, or in thetwo controlling means 30, 31 in common, the pressure-differencecontrolling means maintains the value of |Po−Pi| within 1 bar.

When the difference between Po and Pi is maintained within 1 bar byusing the pressure-difference controlling means, very high or low valuesof Pi or Po do not influence on the reactor tube 2 because the pressuredifference is small between the inner zone and the outer zone of thereactor tube 2.

It is preferred in terms of productivity to maintain the reactionpressure higher than at least 1 bar instead at a vacuum state less than1 bar, if pressure is expressed in absolute unit in the presentinvention.

The feeding rates of fluidizing gas 10 and reaction gas 11 increase withpressure in a nearly proportional manner, based on mole number or massper unit time. Thus, the heat duty in the fluidized bed 4 a for heatingthe reaction gas from an inlet temperature to the temperature requiredfor reaction also increases with the reaction pressure, i.e., Po or Pi.

In case of the reaction gas 11, it is impossible to supply the gas intothe reactor after preheating up to higher than about 350-400° C., i.e.,incipient decomposition temperature. Meanwhile, it is inevitable topreheat the fluidizing gas 10 up to lower than the reaction temperaturebecause impurity contamination is highly probable during a preheatingstep outside the fluidized bed reactor, and the fluidizing gas inletmeans 14 can hardly be insulated to achieve a gas preheating to abovethe reaction temperature. Therefore, difficulties in heating increasewith pressure. When the reaction pressure exceeds about 15 bar, it isdifficult to heat the fluidized bed 4 a as required although a pluralityof heating means 8 a, 8 b are additionally installed at the inner spaceof the reactor shell. Considering these practical limitations, the outerzone pressure (Po) or the inner zone pressure (Pi) is preferred to bemaintained within the range of about 1-15 bar based on the absolutepressure.

According to the pressure within the reactor, the inner pressurecontrolling means 30 and/or the outer pressure controlling means 31 maycomprise a pressure-difference controlling means that can reduce thepressure difference between inside and outside the reactor tube 2. Thiscan be practiced in various ways, some examples of which are describedhereinafter.

The reaction pressure may be set to a high level by using thepressure-difference controlling means without deteriorating thestability of the reactor tube 2, thus enabling to increase both theproductivity and stability of the fluidized bed reactor.

For example, irrespective of the position of installation of the innerpressure controlling means 30 for ultimate connection to the inner zone4, both of the inner pressure controlling means 30 and the outerpressure controlling means 31 may comprise respectivepressure-difference controlling means so that the inner zone pressure(Pi) in the inner zone 4 and the outer zone pressure (Po) in the outerzone 5 may be controlled at predetermined values of pressure, i.e. Pi*and Po*, respectively, satisfying the requirement of |Po*−Pi*|≦1 bar.

For this purpose, the inner pressure controlling means 30 may comprise apressure-difference controlling means that maintains Pi at apredetermined value, Pi*. At the same time, the outer pressurecontrolling means 31 may also comprise a pressure-difference controllingmeans that maintains Po at such a predetermined value, Po*, that therequirement of |Po*−Pi*|≦1 bar is satisfied independently of the height.Likewise, the outer pressure controlling means 31 may comprise apressure-difference controlling means that maintains Po at apredetermined value, Po*. At the same time, the inner pressurecontrolling means 30 may also comprise a pressure-difference controllingmeans that maintains Pi at such a predetermined value, Pi*, that therequirement of |Po*−Pi*|≦1 bar is satisfied independently of the height.

As an another embodiment, irrespective of the position of installationof the inner pressure controlling means 30 for ultimate connection tothe inner zone 4, the inner pressure controlling means 30 may comprise apressure-difference controlling means that maintains Pi at apredetermined value, Pi*, while the outer pressure controlling means 31may comprise a pressure-difference controlling means that controls theouter zone pressure, Po, in accordance with the change of the real-timeinner zone pressure so that the requirement of |Po−Pi|≦1 bar issatisfied independently of the height.

Meanwhile, when determining the values of the control parameters, Pi*and Po*, which are predetermined for maintaining the difference betweenPo and Po within 1 bar, it may be necessary to consider whether or notimpurity components can possibly migrate through a sealing means 41 a,41 b of reactor tube 2.

In assembling the fluidized bed reactor for operation according to thepresent invention, there exists a practical limit that a sufficientdegree of gas-tight sealing may not be obtained at sealing means 41 a,41 b for reactor tube 2. Further, its degree of sealing can be reducedby the shear stress imposed on reactor tube 2 due to fluidization ofsilicon particles 3. In the present invention, the problem of possiblemigration of impurity components between the inner zone 4 and the outerzone 5 through the sealing means 41 a, 41 b may be solved by properlypresetting the values of control parameters, i.e., Pi* and Po*, for thepressure-difference controlling means.

According to the present invention, the pressure control parameters tobe used at the pressure-difference controlling means for controllingpressures in the inner zone and the outer zone, respectively, may bepredetermined based on the analysis of the composition of off-gas 13 orthe gas present in outer zone 5. For example, the pattern of impuritymigration between inner zone 4 and outer zone 5 through the sealingmeans 41 a, 41 b may be deduced based on the component analysis onoff-gas 13 sampled through the gas outlet means 17 or off-gas treatingmeans 34, or that on the gas present in outer zone 5 sampled through anouter zone connecting means 28 or an inert gas connecting means 26 b. Ifoff-gas 13 is verified to comprise the constituent of inert gas 12,which is not supplied into the inner zone, the influx of impurityelements from outer zone 5 into inner zone 4 may be decreased orprevented by presetting the value of Pi* higher than that of Po*, i.e.,Pi*>Po*. In contrast, if the gas discharged out of outer zone 5 isverified to comprise the constituent of off-gas 13 of inner zone 4besides that of inert gas 12, the influx of the impurity elements frominner zone 4 into outer zone 5 may be decreased or prevented bypresetting the value of Po* higher than that of Pi*, i.e., Po*>Pi*.

As mentioned above, although the sealing means 41 a, 41 b of reactortube 2 may not be installed or maintained in a satisfactory mannerduring the assembly or operation of the fluidized bed reactor, anundesirable migration of impurity components between the two zonesthrough the sealing means may be minimized or prevented by appropriateselection of the control parameters for the pressure controlling means.Here, at whatever values Pi* and Po* may be preset in thepressure-difference controlling means, the requirement of |Po*−Pi*|≦1bar should be satisfied according to the present invention.

As another example to accomplish the object of the present invention,the pressure difference, i.e., ΔP=|Po−Pi| may be measured byinterconnecting the inner pressure controlling means 30 and the outerpressure controlling means 31, whereby the pressure-differencecontrolling means may maintain the value of ΔP within the range of 0 to1 bar, irrespective of the position of inner zone 4 selected formeasurement of Pi, by controlling the inner pressure controlling means30 and/or the outer pressure controlling means 31 in a manual,semi-automatic or automatic way.

As still another example to accomplish the object of the presentinvention, the pressure-difference controlling means may comprise anequalizing line, which spatially interconnects a connecting pipecomprised in the inner pressure controlling means 30 and a connectingpipe comprised in the outer pressure controlling means 31. A connectingpipe, which is comprised in the inner pressure controlling means 30 andconstitutes the equalizing line 23, may be installed at a positionselected for spatial connection with inner zone 4, including but notlimited to an inner zone connecting means 24, 25; a fluidizing gas inletmeans 14, 14′; a reaction gas inlet means 15; a particle outlet means16; a gas outlet means 17; or a seed crystals inlet means 18, all ofwhich are spatially exposed to the inner zone in a direct or indirectmanner. Meanwhile, a connecting pipe, which is comprised in the outerpressure controlling means 31 and constitutes an equalizing line 23, maybe installed at a position selected for spatial connection with outerzone 5, including but not limited to an outer zone connecting means 28or an inert gas connecting means 26 a, 26 b comprising the inert gasinlet means and the inert gas outlet means, all of which are coupledwith the reactor shell and spatially exposed to the outer zone in adirect or indirect manner.

The equalizing line 23, which interconnects spatially the inner pressurecontrolling means 30 and outer pressure controlling means 31, may bereferred to as a simplest form of the pressure-difference controllingmeans because it may always maintain the pressure difference between twointerconnected zones 4, 5 at nearly zero.

Despite this advantage, when constituting the pressure-differencecontrolling means by the equalizing line 23 alone, gas and impuritycomponents may undesirably be interchanged between two zones 4, 5. Inthis case, the impurity elements generated or discharged from aninsulating material or a heating means installed in outer zone 5 maycontaminate the inner zone 4, especially the polycrystalline siliconparticles. Likewise, silicon fine powders or components of residualreaction gas or reaction byproduct discharged from the inner zone 4 maycontaminate the outer zone 5.

Therefore, when the equalizing line 23 is used as thepressure-difference controlling means, a pressure equalizing means,which can decrease or prevent the possible interexchange of gas andimpurity components between two zones 4, 5, may be further added to theequalizing line 23. The pressure equalizing means may comprise at leastone means selected from a check valve, a pressure equalizing valve, a3-way valve, a filter for separating particles, a damping container, apacked bed, a piston, an assistant control fluid, and a pressurecompensation device using separation membrane, which, respectively, isable to prevent the possible interexchange of gas and impuritycomponents without deteriorating the effect of pressure equalization.

Besides, the pressure-difference controlling means may comprise a manualvalve for controlling pressure or flow rate, or may further comprisea(n) (semi-)automatic valve that performs a(n) (semi-)automatic controlfunction according to a predetermined value of pressure or pressuredifference. These valves may be installed in combination with a pressuregauge or a pressure indicator that exhibits a pressure or pressuredifference.

The pressure gauge or the pressure indicator is available commerciallyin the form of either analogue, digital or hybrid device, and may beincluded in an integrated system of data acquisition, storage andcontrol, if combined with a data processing means such as a signalconverter or a signal processor, etc., and/or with a local controller, adistributed controller or a central controller including a circuit forperforming an arithmetic operation.

Illustrative embodiments according to the Drawings herein are explainedhereinafter in terms of the application of the pressure-differencecontrolling means for decreasing the pressure difference between insideand outside the reactor tube 2 in the fluidized bed reactor forpreparing granular polycrystalline silicon.

DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows the characteristics of the method forpreparing granular polycrystalline silicon according to the presentinvention.

FIG. 2 is a cross-sectional view of a high-pressure fluidized bedreactor for preparing granular polycrystalline silicon, in which severalembodiments of the present invention are illustrated in a comprehensiveway.

FIG. 3 is a cross-sectional view of a high-pressure fluidized bedreactor for preparing granular polycrystalline silicon, in which someother embodiments according to the present invention are illustrated ina comprehensive way.

CODE EXPLANATION OF THE DRAWINGS

 1: Reactor shell  2: Reactor tube  3: silicon particles  3a: Siliconseed crystals  3b: Silicon product particles  4: Inner zone  5: Outerzone  6: Insulating material  7: Liner  8: Heater  9: Electric energysupplying 10: Fluidizing gas means 11: Reaction gas 12: Inert gas 13:Off-gas 14: Fluidizing gas inlet means 15: Reaction gas inlet means 16:Particle outlet means 17: Gas outlet means 18: Silicon seed crystalsinlet means 19: Gas distributing means 23: Equalizing line 24, 25: Innerzone connecting 26: Inert gas connecting means means 27: On/off valve28: Outer zone connecting means 30: Inner pressure controlling 31: Outerpressure controlling means means 32: Pressure-difference gauge 33:Fluctuation reducing means 34: Off-gas treating means 35: Gas analyzingmeans 36: Filter 41: Sealing means E: Electric source

BEST MODE

The present invention is described more specifically by the followingExamples. Examples herein are meant only to illustrate the presentinvention, but in no way to limit the scope of the claimed invention.

EXAMPLE 1

Hereunder is provided a description of one embodiment where the innerzone pressure (Pi) and the outer zone pressure (Po) are independentlycontrolled at predetermined values, Pi* and Po*, respectively, and thedifference between the values of the inner zone pressure and the outerzone pressure is thereby maintained within the range of 0 to 1 bar.

As illustrated in FIGS. 2 and 3, an inner pressure controlling means 30may be constituted by interconnecting a first pressure control valve 30b with a gas outlet means 17 through an off-gas treating means 34 forremoving fine silicon particles, which are interconnected with eachother by a connecting pipe. The pressure of the upper part of the innerzone 4 may be controlled at a predetermined value, Pi*, by using thefirst pressure control valve 30 b which behaves as an element of apressure-difference controlling means.

Meanwhile, as illustrated in FIG. 2, an outer pressure controlling means31 may be constituted by interconnecting an inert gas connecting means26 a, a fourth pressure gauge 31 a′ and a fourth pressure control valve31 b′. Although being separately installed in FIG. 2, the fourthpressure gauge 31 a′ and the fourth pressure control valve 31 b′ may beintegrated with each other by a circuit, and thus be constituted as asingle device that can measure and control pressure at the same time.

When the inner pressure controlling means 30 is connected to an upperpart of the inner zone 4 c, the pressure of which is lower than those inor below the fluidized bed, it is preferred to preset Pi* and Po* sothat the condition of Po*≧Pi* may be satisfied.

In this Example, the outer zone pressure may be controlled at apredetermined value, Po*, so that the condition of 0 bar≦(Po*−Pi*)≦1 barmay be satisfied, by using the fourth pressure gauge 31 a′ and thefourth pressure valve 31 b′ both of which behave as elements of apressure-difference controlling means.

However, when an inert gas 12 component is detected in the off-gas 13 bya gas analyzing means 35, which may be installed as illustrated in FIG.3, Po* may be preset at a lower value so that the condition of Pi*≧Po*may be satisfied.

Meanwhile, the inner pressure controlling means 30 and the outerpressure controlling means 31 may further comprise their ownpressure-difference controlling means, respectively, thus enabling thecondition of 0 bar≦|Po−Pi|≦1 bar to be satisfied, where Po and Pi arevalues of pressure measured in connection with the outer zone 5 and anyposition in the inner zone 4, respectively.

EXAMPLE 2

Hereunder is provided a description of another embodiment where theinner zone pressure (Pi) and the outer zone pressure (Po) areindependently controlled at the predetermined values, Pi* and Po*,respectively, and the difference between the values of the inner zonepressure and the outer zone pressure is thereby maintained within therange of 0 to 1 bar.

As illustrated in FIGS. 2 and 3, an inner pressure controlling means 30may be constituted by interconnecting a first pressure control valve 30b with the gas outlet means 17 through the off-gas treating means 34 forremoving fine silicon particles, which are interconnected with eachother by a connecting pipe. The pressure of the upper part of the innerzone 4 may be controlled at a predetermined value, Pi*, by using thefirst pressure control valve 30 b which behaves as an element of apressure-difference controlling means.

Meanwhile, as illustrated in FIG. 2, an outer pressure controlling means31 may be constituted by interconnecting an inert gas connecting means26 b, an on/off valve 31 c, a third pressure gauge 31 a and a thirdpressure control valve 31 b. Although being separately installed in FIG.2, the third pressure gauge 31 a and the third pressure control valve 31b may be integrated with each other by a circuit, and thus beconstituted as a single device that can measure and control pressure atthe same time.

Unlike in Example 1, the supply of an inert gas 12 may be controlled bythe third pressure control valve 31 b in combination with the Pocontrol, instead of connecting the inert gas connecting means 26 a to apressure-difference controlling means such as the fourth pressure gauge31 a′ and the fourth pressure valve 31 b′

When the inner pressure controlling means 30 is connected to an upperpart of the inner zone 4 c, the pressure of which is lower than those inor below the fluidized bed, it is preferred to preset Pi* and Po* sothat the condition of Po*≧Pi* may be satisfied.

In this Example, the outer zone pressure may be controlled at apredetermined value, Po*, so that the condition of 0 bar≦(Po*−Pi*)≦1 barmay be satisfied, by the third pressure gauge 31 a and the thirdpressure control valve 31 b both of which behave as elements of apressure-difference controlling means.

However, when an inert gas 12 component is detected in the off-gas 13 bya gas analyzing means 35, which may be installed as illustrated in FIG.3, Po* may be preset at a lower value so that the condition of Pi*≧Po*may be satisfied.

Meanwhile, the inner pressure controlling means 30 and the outerpressure controlling means 31 may further comprise their ownpressure-difference controlling means, respectively, thus enabling thecondition of 0 bar≦|Po−Pi|≦1 bar to be satisfied, where Po and Pi arevalues of pressure measured in connection with the outer zone 5 and anyposition in the inner zone 4, respectively.

EXAMPLE 3

Hereunder is provided a description of one embodiment where the innerzone pressure (Pi) is controlled according to the change of the outerzone pressure (Po), and the difference between the values of the innerzone pressure and the outer zone pressure is thereby maintained withinthe range of 0 to 1 bar.

As illustrated in FIGS. 2 and 3, a gas outlet means 17, an off-gastreating means 34 for removing fine silicon particles and a firstpressure control valve 30 b are interconnected with each other by aconnecting pipe. Then an inner pressure controlling means 30 may beconstituted by interconnecting the connecting pipe with an on/off valve27 e and a pressure-difference gauge 32.

Meanwhile, as illustrated in FIG. 2, an outer pressure controlling means31 may be constituted by interconnecting an inert gas connecting means26 b and a pressure-difference gauge 32, which are interconnected witheach other by the connecting pipe. Here an inert gas 12 may be suppliedto the outer zone through an inert gas connection means 26 a.

In the present example, the pressure-difference gauge 32 is be a commonelement for both the inner pressure controlling means 30 and the outerpressure controlling means 31. Besides the pressure control valve 31 b,31 b′ may be omitted.

When the inner pressure controlling means 30 and the outer pressurecontrolling means 31 are constituted as described above, the differencebetween the outer zone pressure (Po) and the inner pressure (Pi) inupper part of the inner zone can be maintained to be lower than 1 barindependently of the change of the outer zone pressure (Po) by using thepressure-difference gauge 32 and the first pressure control valve 30 bboth of which behave as elements of a pressure-difference controllingmeans.

Further, the inner pressure controlling means 30 may be connected to anupper part of the inner zone 4 c, the pressure of which is lower thanthose in or below the fluidized bed, and it is preferred to control thefirst pressure control valve 30 b so that the condition of Po≧Pi may besatisfied.

However, when an inert gas 12 component may be detected in the off-gas13 by a gas analyzing means 35, which may be installed as illustrated inFIG. 3, the first pressure control valve 30 b may be controlled so thatthe condition of Pi≧Po may be satisfied.

Following the aforementioned constitution and operation of the fluidizedbed reactor, the condition of 0 bar≦|Po−Pi|≦1 bar may be satisfied atany position in the inner zone 4.

Meanwhile, the object of the present Example may be accomplished eitherby automatic control of the integrated circuit of thepressure-difference gauge 32 and the first pressure control valve 30 b,or by manual operation of the first pressure control valve 30 b inaccordance with the values of ΔP measured with the pressure-differencegauge 32.

Instead of the pressure-difference gauge 32, only a first pressure gauge30 a and a third pressure gauge 31 a may be installed as the innerpressure controlling means 30 and the outer pressure controlling means31, respectively. Alternatively, the pressure-difference controllingmeans may be further corrected or improved by equipping a first pressuregauge 30 a and a third pressure gauge 31 a in the inner pressurecontrolling means 30 and the outer pressure controlling means 31,respectively, in addition to the pressure-difference gauge 32.

EXAMPLE 4

Hereunder is provided a description of another embodiment where theinner zone pressure (Pi) is controlled according to the change of theouter zone pressure (Po), and the difference between the values of theinner zone pressure and the outer zone pressure is thereby maintainedwithin the range of 0 to 1 bar.

As illustrated in FIGS. 2 and 3, an inner pressure controlling means 30may be constituted by interconnecting a first pressure control valve 30b with the gas outlet means 17 through the off-gas treating means 34 forremoving fine silicon particles, which are interconnected with eachother by a connecting pipe.

Meanwhile, as illustrated in FIG. 2, an outer pressure controlling means31 may be constituted by interconnecting an inert gas connecting means26 a for supplying an inert gas 12 and a fourth pressure gauge 31 a′,which are interconnected with each other by the connecting pipe. Here,an inert gas 12 may be discharged through an inert gas connection means26 b. Besides the pressure control valve 31 b, 31 b′ in FIG. 2 may beomitted.

When the inner pressure controlling means 30 and the outer pressurecontrolling means 31 are constituted as described above, the differencebetween the outer zone pressure (Po) and the inner pressure (Pi) in theupper part of the inner zone 4 c can be maintained to be lower than 1bar independently of the change of the outer zone pressure (Po) by usingthe fourth pressure gauge 31 a′ and the first pressure control valve 30b both of which behave as elements of a pressure-difference controllingmeans.

Further, since the inner pressure controlling means 30 may be connectedto an upper part of the inner zone 4 c, the pressure of which is lowerthan those in or below the fluidized bed, it is preferred to control thefirst pressure control valve 30 b so that the condition of Po≧Pi may besatisfied.

However, when an inert gas 12 component is detected in an off-gas 13 bya gas analyzing means 35, which may be installed as illustrated in FIG.3, the first pressure control valve 30 b may be controlled so that thecondition of Pi≧Po may be satisfied.

Following the aforementioned constitution and operation of the fluidizedbed reactor, the condition of 0 bar≦|Po−Pi|≦1 bar may be satisfied atany position in the inner zone 4.

Meanwhile, the object of the present Example may be accomplished eitherby automatic control of the integrated circuit of the fourth pressuregauge 31 a′ and the first pressure control valve 30 b, or by manualoperation of the first pressure control valve 30 b in accordance withthe pressure value measured with the fourth pressure gauge 31 a′.

Instead of connecting a fourth pressure gauge 31 a′ to the inert gasconnecting means 26, the outer pressure controlling means 31 may also beconstituted by connecting a fifth pressure gauge 31 p to an outer zoneconnecting means 28 as illustrated in FIG. 2 or a fifth pressure gauge31 p connected to the outer zone connecting means 28 a as illustrated inFIG. 3 or a third pressure gauge 31 a connected to an inert gasconnecting means 26 b as illustrated in FIG. 3. Then, the respectivepressure gauge employed in the outer pressure controlling means 31 mayalso behave as another element of the pressure-difference controllingmeans. Accordingly, the object of the present Example may beaccomplished by regulating the first pressure control valve 30 b, whichbehaves as an element of the pressure-difference controlling means thatis comprised in the inner pressure controlling means 30, in accordancewith the other element of the pressure-difference controlling means thatis comprised in a variety of outer pressure controlling means 31.

EXAMPLE 5

Hereunder is provided a description of one embodiment where the outerzone pressure (Po) is controlled according to the change of the innerzone pressure (Pi), and the difference between the values of the innerzone pressure and the outer zone pressure is thereby maintained withinthe range of 0 to 1 bar.

As illustrated in FIGS. 2 and 3, an inner pressure controlling means 30may be constituted by interconnecting an on/off valve 27 d and apressure-difference gauge 32 with an outer zone connecting means 25instead of the gas outlet means 17, which are interconnected with eachother by a connecting pipe.

Meanwhile, as illustrated in FIG. 2, the outer pressure controllingmeans 31 may be constituted by interconnecting a third pressure controlvalve 31 b and pressure-difference gauge 32 with an inert gas connectingmeans 26 b, which are interconnected with each other by the connectingpipe. This case corresponds to the case of constitution where the on/offvalves 27 c, 27 e are closed. In the present example, thepressure-difference gauge 32 is a common element for both the innerpressure controlling means 30 and the outer pressure controlling means31.

When the inner pressure controlling means 30 and the outer pressurecontrolling means 31 are constituted as described above, the differencebetween the outer zone pressure (Po) and the inner pressure (Pi) in theupper part of the inner zone 4 c can be maintained to be lower than 1bar independently of the change of the inner zone pressure (Pi) by usingthe pressure-difference gauge 32 and the third pressure control valve 31b both of which behave as elements of a pressure-difference controllingmeans.

Further, since the inner pressure controlling means 30 may be connectedto an upper part of the inner zone 4 c the pressure of which is lowerthan those in or below the fluidized bed, the third pressure controlvalve 31 b may be controlled so that the condition of Po≧Pi may besatisfied.

However, when an inert gas 12 component is detected in an off-gas 13 bya gas analyzing means 35 which may be installed as illustrated in FIG.3, the first pressure control valve 30 b may be controlled so that thecondition of Pi≧Po may be satisfied.

Following the aforementioned constitution and operation of the fluidizedbed reactor, the condition of 0 bar≦|Po−Pi|≦1 bar may be satisfied atany position in the inner zone 4.

Meanwhile, the object of the present Example may be accomplished eitherby automatic control of the integrated circuit of thepressure-difference gauge 32 and the third pressure control valve 31 b,or by manual operation of the third pressure control valve 31 b inaccordance with the ΔP value measured with the pressure-difference gauge32.

Instead of the pressure-difference gauge 32, only a first pressure gauge30 a and a third pressure gauge 31 a may be installed as the innerpressure controlling means 30 and the outer pressure controlling means31, respectively. Alternatively, the pressure-difference controllingmeans may be further corrected or improved by equipping a first pressuregauge 30 a and a third pressure gauge 31 a in the inner pressurecontrolling means 30 and the outer pressure controlling means 31,respectively, in addition to the pressure-difference gauge 32.

The outer pressure controlling means in this Example may be constitutedin another form. For example, instead of interconnection of the pressurecontrol valve 31 b and pressure-difference gauge 32 with the inert gasconnecting means 26 b in FIG. 2, the outer pressure controlling meansmay also be constituted by interconnecting the fourth pressure valve 31b′ and the pressure-difference gauge 32 with the inert gas connectingmeans 26 a for supplying the inert gas, which are interconnected witheach other by a connecting pipe. If corresponding elements of thepressure-difference controlling means is further replaced together withsuch modification of the outer pressure controlling means, the object ofthe present Example may also be accomplished thereby.

EXAMPLE 6

Hereunder is provided a description of another embodiment where theouter zone pressure (Po) is controlled according to the change of theinner zone pressure (Pi), and the difference between the values of theinner zone pressure and the outer zone pressure is thereby maintainedwithin the range of 0 to 1 bar.

As illustrated in FIG. 3, the inner pressure controlling means 30 may beconstituted by interconnecting a second pressure gauge 30 a′ and apressure-difference gauge 32 with a fluidizing gas inlet means 14, whichare interconnected with each other by a connecting pipe and/or byelectrical integration.

Meanwhile, as illustrated in FIG. 3, the outer pressure controllingmeans 31 may be constituted by interconnecting a third pressure gauge 31a and a pressure-difference gauge 32, both of which are connected to aninert gas connecting means 26 b, with a second pressure control valve 30b′ which is connected to an inert gas connecting means 26 a. Here, theinterconnection may be achieved by the connecting pipe and/or byelectrical integration.

In the present example, the pressure-difference gauge 32 is a commonelement for both the inner pressure controlling means 30 and the outerpressure controlling means 31. The pressure-difference gauge 32 exhibitsa physical and/or electrical signal for the difference between Pi andPo, which are measured with the second pressure gauge 30 a′ and thethird pressure gauge 31 a, respectively.

A fluctuation reducing means 33 may further be applied to thepressure-difference gauge because the fluidization of silicon particlesin the fluidized bed naturally introduces fluctuation in the value of Pimeasured by the second pressure gauge 30 a′. The fluctuation reducingmeans 33 may comprise a pressure fluctuation damping (or buffering)means such as a physical device or a software-based device thattransforms the fluctuating signals into an average Pi value for apredetermined short period of time (e.g., one second).

Then, by using the pressure-difference gauge 32 and the second pressurecontrol valve 30 b′ both of which behave as elements of apressure-difference controlling means, the difference between the outerzone pressure (Po) and the inner zone pressure (Pi) is maintained to belower than 1 bar independently of the change of the inner zone pressure(Pi) measured through the fluidizing gas inlet means 14 in connectionwith the inner zone.

Further, since the inner pressure controlling means 30 may be connectedto a lower part of the fluidized bed, the pressure of which is higherthan that in upper part of the inner zone 4 c, the second pressurecontrol valve 30 b′ may be controlled so that the condition of Po≦Pi maybe satisfied.

However, when an off-gas 13 component is detected in an inert gas 12′ bya gas analyzing means 35, which may be installed as illustrated in FIG.3, the second pressure control valve 30 b′ may be controlled so that thecondition of Po≧Pi may be satisfied.

Following the aforementioned constitution and operation of the fluidizedbed reactor, the condition of 0 bar≦|Po−Pi|≦1 bar may be satisfied atany position in the inner zone 4.

Meanwhile, the object of the present Example may be accomplished eitherby automatic control of the integrated circuit of thepressure-difference gauge 32 and the second pressure control valve 30b′, or by manual operation of the second pressure control valve 30 b′ inaccordance with the ΔP value measured with the pressure-difference gauge32.

Further, on behalf of the third pressure gauge 31 a in connection withthe inert gas connecting means 26 b, another outer pressure gauge may beconnected to the pressure-difference gauge 32 for achieving the objectof the present Example. For example, the outer pressure gauge may alsobe selected from the fifth pressure gauge 31 p in connection with theouter zone connecting means 28 a or a sixth pressure gauge 31 q inconnection with the inert gas connecting means 26 a.

EXAMPLE 7

Hereunder is provided a description of one embodiment where thedifference between the values of the inner zone pressure and the outerpressure is maintained within the range of 0 to 1 bar by using anequalizing line spatially interconnecting the inner zone and the outerzone.

As illustrated in FIG. 2, the equalizing line 23 may be composed of aconnecting pipe which spatially interconnects an inner zone connectingmeans 25 with an inert gas connecting means 26 b.

In this case, the inner pressure controlling means 30 may be basicallycomposed of the inner zone connecting means 25 and the connecting pipe,and may further comprise an on/off valve 27 d and a first pressure gauge30 a as illustrated in FIG. 2. Meanwhile, the outer pressure controllingmeans 31 may be basically composed of a connecting means, which isselected from an inert gas connecting means 26 a or an outer zoneconnecting means 28, and the connecting pipe, and may further comprisean on/off valve 31 c and a third pressure gauge 31 a as illustrated inFIG. 2.

In the present Example, an equalizing line 23 is composed of the twoconnecting pipes that constitute the inner pressure controlling means 30and the outer pressure controlling means 31, respectively. Therefore,the equalizing line 23 behaves, by itself, as a pressure-differencecontrolling means. Spatially interconnecting the upper part of the innerzone 4 c with the outer zone 5, the equalizing line 23 naturallyprevents an apparent pressure difference between these two zones.

The pressure difference between Pi, measured at a lower part of thefluidized bed 4 a where Pi is highest in the bed, and Po, measured at anupper part of the inner zone 4 c, is usually below 1 bar. Thus, if theequalizing line 23 is used as the pressure-difference controlling means,the pressure difference between Pi and Po, i.e., between inside andoutside of the reactor tube 2 may be maintained below 1 bar irrespectiveof the measurement point of Pi.

The object of the present Example may also be accomplished by selectinga space in connection with a gas outlet means 17, instead of the innerzone connecting means 25, for constituting the inner pressurecontrolling means 30.

Meanwhile, the effect of pressure equalization of Pi and Po attributedto the equalizing line 23, which is a pressure-difference controllingmeans in the present Example, may also be obtained when a pressureequalizing valve 27 c is further equipped at the equalizing line 23enabling spatial partition of the inner zone and the outer zone.

EXAMPLE 8

Hereunder is provided a description of another embodiment where thedifference between the values of the inner zone pressure and the outerzone pressure is maintained within the range of 0 to 1 bar by using anequalizing line spatially interconnecting the inner zone and the outerzone

As illustrated in FIG. 3, the equalizing line 23 may be composed of aconnecting pipe which spatially interconnects an inner zone connectingmeans 25 and an outer zone connecting means 28 b. In this case, theinner pressure controlling means 30 may be basically composed of theinner zone connecting means 25 and the connecting pipe. Meanwhile, theouter pressure controlling means 31 may be basically composed of theouter zone connecting means 28 b and the connecting pipe.

In the present Example, an equalizing line 23 is composed of the twoconnecting pipes that constitute the inner pressure controlling means 30and the outer pressure controlling means 31, respectively. Therefore,the equalizing line 23 behaves, by itself, as a pressure-differencecontrolling means. Spatially interconnecting the upper part of the innerzone 4 c with the outer zone 5, the equalizing line 23 naturallyprevents an apparent pressure difference between these two zones.

The pressure difference between Pi, measured at a lower part of thefluidized bed 4 a where Pi is highest in the bed, and Po, measured at anupper part of the inner zone 4 c, is usually below 1 bar. Thus, if theequalizing line 23 is used as the pressure-difference controlling means,the pressure difference between Pi and Po, i.e., between inside andoutside of the reactor tube 2 may be maintained below 1 bar irrespectiveof the measurement point of Pi.

Meanwhile, to prevent the migration of impure particles and componentsthrough the equalizing line 23, a filter 36 and/or an on/off valve 27 dmay be further equipped at the equalizing line 23 as illustrated in FIG.3.

EXAMPLE 9

Hereunder is provided a description of still another embodiment wherethe difference between the values of the inner zone pressure and theouter zone pressure is maintained within the range of 0 to 1 bar byusing an equalizing line spatially interconnecting the inner zone andthe outer zone.

As illustrated in FIG. 3, the equalizing line 23 may be composed of aconnecting pipe which spatially interconnects a gas outlet means 17 withan inert gas connecting means 26 b.

In this case, the inner pressure controlling means 30 may be basicallycomposed of the gas outlet means 17, an off-gas treating means 34 andthe connecting pipe, and may further comprise a first pressure gauge 30a, an on/off valve 31 d, a filter 36, etc., as illustrated in FIG. 3.Meanwhile, the outer pressure controlling means 31 may be basicallycomposed of a connecting means, which is selected among an inert gasconnecting means 26 a or an outer zone connecting means 28, and theconnecting pipe, and may further comprise an on/off valves 31 b, 31 e,31 f, 31 g, a gas analyzing means 35 and a third pressure gauge 31 a,etc., as illustrated in FIG. 3.

In the present Example, an equalizing line 23 is composed of the twoconnecting pipes that constitute the inner pressure controlling means 30and the outer pressure controlling means 31, respectively. Therefore,the equalizing line 23 behaves, by itself, as a pressure-differencecontrolling means. Spatially interconnecting the upper part of the innerzone 4 c with the outer zone 5, the equalizing line 23 naturallyprevents an apparent pressure difference between these two zones.

The pressure difference between Pi, measured at a lower part of thefluidized bed 4 a where Pi is highest in the bed, and Po, measured at anupper part of the inner zone 4 c, is usually below 1 bar. Thus, if theequalizing line 23 is used as the pressure-difference controlling means,the pressure difference between Pi and Po, i.e., between inside andoutside of the reactor tube 2 may be maintained below 1 bar irrespectiveof the measurement point of Pi.

The object of the present Example may also be accomplished when areaction gas inlet means 15 is interconnected with the outer zone 5 byselecting a space in connection with a reaction gas inlet means 15,instead of the gas outlet means 17, for constituting the inner pressurecontrolling means 30.

Meanwhile, the effect of pressure equalization of Pi and Po attributedto the equalizing line 23, which is a pressure-difference controllingmeans in the present Example, may also be obtained when a pressureequalizing valve 27 c in FIG. 3 is further equipped at the equalizingline 23 enabling spatial partition of the inner zone and the outer zone.

EXAMPLE 10

Hereunder is provided a description of still another embodiment wherethe outer zone pressure (Po) is controlled according to the change ofthe inner zone pressure (Pi), and the difference between the values ofthe inner zone pressure and the outer zone pressure is therebymaintained within the range of 0 to 1 bar.

In the present Example, an average value of the inner zone pressure,Pi(avg), may be estimated from the two values of pressure measured attwo spaces which are in spatial connection with a fluidizing gas inletmeans 14 and a gas outlet means 17 independently. Then, Po may becontrolled according to the estimated value of Pi(avg), thus maintainingthe difference between the values of Pi and Po within 1 bar, preferably0.5 bar.

In the present Example, a second pressure gauge 30 a′ and a firstpressure gauge 30 a are installed in connection with a fluidizing gasinlet means 14 and a gas outlet means 17, respectively. The innerpressure controlling means 30 may be constituted as an integratedcircuit of a pressure-difference gauge 32 of FIG. 3 and a controllercomprising an arithmetic processor, where the controller generates anestimated value of Pi(avg) based on the real-time measurements of thetwo pressure gauges 30 a′, 30 a. Meanwhile, as illustrated in FIG. 3, anouter pressure controlling means 31 may be constituted as an integratedcircuit of the pressure-difference gauge 32 as well as a second pressurecontrol valve 30 b′ and a third pressure gauge 31 a which are connectedto an inert gas connecting means 26 a and an inert gas connecting means26 b, respectively. Here, the pressure-difference gauge 32 exhibits thedifference between Pi(avg) and Po, and generates an electric signalcorresponding to the difference, thus operating the second pressurecontrol valve 30 b′. Therefore, being a common element for both theinner pressure controlling means 30 and the outer pressure controllingmeans 31, the software-based function of the pressure-difference gauge32 may be coupled into the controller for estimation of Pi(avg).

Because the value of Pi measured by the second pressure gauge 30 a′fluctuates depending on the fluidization state of the fluidized bed, thecontroller comprising an arithmetic processor for estimation of Pi(avg)may further comprise a software-based damping means that generatestime-averaged values of pressure, Pi*(avg), at an interval of, forexample, 10 seconds or 1 minute based on the fluctuating real-timevalues of Pi. This damping means may allow a smooth operation of thesecond pressure control valve 30 b′ based on the time-averaged valueinstead of the fluctuating Pi.

Using the controller comprising an arithmetic processor and the secondpressure control valve 30 b′ as a pressure-difference controlling means,it is possible to control the outer zone pressure (Po) according to thechange of the time-average of Pi values measured at different positionsin connection with the inner zone, and then to maintain the differenceof Po from and Pi(avg) or Pi*(avg) within the range of 0 to 1 bar.

The manipulation of the second pressure control valve 30 b′ forcontrolling the outer zone pressure according to the average value ofthe inner zone pressure may be adjusted following a gas-componentanalysis on the off-gas through a gas outlet means 17 or the off-gastreating means 34 and/or on the gas discharged from the outer zonethrough the outer zone connecting means 28 or an inert gas connectingmeans 26 b. If a large amount of an inert gas component is detected inthe off-gas, it is preferred to lower Po, thus decreasing the migrationof impurity into the inner zone 4 from the outer zone 5. On thecontrary, if an off-gas 13 component is detected in the gas from theouter zone besides an inert gas 12, it is preferred to raise Po, thusdecreasing the migration of impurity into the outer zone 5 from theinner zone 4. Nonetheless, according to the present Example, thecondition of |Po−Pi*(avg)|≦1 bar should be satisfied irrespective ofconditions for controlling Po. If the impurity component is notdetected, it is preferred to manipulate the second pressure controlvalve 30 b′ so that Po may be substantially the same with Pi*(avg).Therefore, it is possible to minimize or prevent the undesirablemigration of impurity by controlling the pressure difference between theinner zone 4 and the outer zone 5, although the sealing means 41 a, 41 bfor reactor tube 2 are not maintained perfect during the operation ofthe fluidized bed reactor.

The object of the present Example may also be accomplished byconstituting the outer pressure controlling means 31 in a different way.For example, instead of the third pressure gauge 31 a connected to theinert gas connecting means 26 b, a fifth pressure gauge 31 p or a sixthpressure gauge 31 q, which are connected to an outer zone connectingmeans 28 a or an inert gas connecting means 26 a, respectively, may beselected as the pressure gauge to be connected to thepressure-difference gauge 32. Further, instead of the second pressurecontrol valve 30 b′ connected to the inert gas connecting means 26 a, athird pressure control valve 31 b connected to the inert gas connectingmeans 26 b may be selected as the pressure control valve.

Meanwhile, the object of the present Example may also be accomplished byconstituting the inner pressure controlling means 30 in a different way.For example, instead of the second pressure gauge 30 a′ connected to thefluidizing gas inlet means 14, a pressure gauge in spatial connectionwith a silicon product particle outlet means 16 may be selected formeasurement of Pi(avg) together with the first pressure gauge 30 aconnected to the gas outlet means 17.

Besides the aforementioned Examples, the inner pressure controllingmeans 30, the outer pressure controlling means 31 and thepressure-difference controlling means may be constituted in a variety ofmanners for preparation of granular polycrystalline silicon according tothe present invention.

INDUSTRIAL APPLICABILITY

As set forth above, the method according to the present invention forpreparing granular polycrystalline silicon using the fluidized bedreactor have the superiority as follows.

1. Bulk production of granular polycrystalline silicon can be carriedout according to the process using the fluidized bed reactor as setforth herein.

2. The pressure difference between both sides of the reactor tube ismaintained so low that a high-pressure silicon deposition is possiblewithout deteriorating the physical stability of the reactor tube, thusenabling to fundamentally prevent the damage of the reactor tube due tothe pressure difference, and to improve long-term stability of thereactor.

3. The pressure difference between the inner zone and the outer zone maybe maintained within a predetermined range at a relatively low costwithout continuously providing a large amount of inert gas into theouter zone of the reactor.

4. High reaction temperature required for silicon deposition can beeasily maintained by the heating means employed for heating the siliconparticle bed.

5. The process as set forth herein can be utilized for economical andenergy-efficient production of high-purity polycrystalline silicon withminimized impurity contamination and enhanced productivity.

6. The outer zone of the reactor is maintained under an inert gasatmosphere and the inert gas may be discharged through a separate exit.Thus, although an insulating material and optionally a heater areinstalled in the outer zone and the outer zone may comprise additionalpartitioning means in a radial or vertical direction, it is possible todecrease remarkably the possibility that impurity from these componentscan migrate into the inner zone and deteriorate the quality ofpolycrystalline silicon product.

7. The long-term stability of the reactor may be improved remarkablybecause any thermal degradation in terms of chemical and physicalproperties of those additional components in the outer zone is lessprobable under the inert gas atmosphere.

1. A method for preparing polycrystalline silicon using a fluidized bedreactor, comprising: (a) employing a fluidized bed reactor wherein areactor tube is vertically placed within a reactor shell so as to beencompassed by the reactor shell, whereby dividing an inner space of thereactor shell into an inner zone formed within the reactor tube and anouter zone formed in between the reactor shell and the reactor tube,wherein a silicon particle bed is formed and silicon deposition occursin the inner zone while a silicon particle bed is not formed and silicondeposition does not occur in the outer zone; (b) directly or indirectlymeasuring and/or controlling an inner zone pressure using an innerpressure controlling means, directly or indirectly measuring and/orcontrolling an outer zone pressure using an outer pressure controllingmeans, and maintaining the difference between the inner zone pressureand the outer zone pressure within 1 bar using a pressure-differencecontrolling means; (c) introducing a fluidizing gas into the siliconparticle bed using a fluidizing gas inlet means; (d) introducing asilicon atom-containing reaction gas into the silicon particle bed usinga reaction gas inlet means; (e) introducing an inert gas into the outerzone, whereby maintaining a substantially inert gas atmosphere in theouter zone; (f) heating the silicon particle bed using a heating meansinstalled in the inner zone and/or the outer zone; (g) dischargingpolycrystalline silicon particles prepared within the inner zone to theoutside of the fluidized bed reactor; (h) discharging an off-gasincluding a fluidizing gas that passes through the silicon particle bed,a non-reacted reaction gas and a byproduct gas to the outside of thefluidized bed reactor.
 2. The method of claim 1, wherein the reactiongas is a silicon atom-containing gas selected from the group consistingof monosilane, dichlorosilane, trichlorosilane, silicon tetrachlorideand a mixture thereof.
 3. The method of claim 2, wherein the reactiongas further comprises at least one gas selected from the groupconsisting of hydrogen, nitrogen, argon, helium, hydrogen chloride and amixture thereof.
 4. The method of claim 1, wherein the fluidizing gas isa gas selected from the group consisting of hydrogen, nitrogen, argon,helium, hydrogen chloride, silicon tetrachloride and a mixture thereof.5. The method of claim 1, wherein the inert gas comprises at least onegas selected from the group consisting of hydrogen, nitrogen, argon andhelium.
 6. The method of claim 1, wherein the outer zone pressure (Po)or the inner zone pressure (Pi) is maintained within the range of 1-15bar.
 7. The method of claim 1, wherein the outer zone pressure (Po) maybe controlled in the range of between maximum and minimum pressurevalues measurable in the inner zone.
 8. The method of claim 1, whereinthe difference between the outer zone pressure (Po) and the inner zonepressure (Pi) is maintained so as to satisfy the condition of 0bar≦(Pi−Po)≦1 bar, when the inner pressure controlling means isspatially connected to the inner zone through at least one meansselected from the group consisting of a fluidizing gas inlet means, areaction gas inlet means, a silicon particle outlet means and an innerzone connecting means, which are spatially connected to the siliconparticle bed.
 9. The method of claim 1, wherein the difference betweenthe outer zone pressure (Po) and the inner zone pressure (Pi) ismaintained so as to satisfy the condition of 0 bar≦(Po−Pi)≦1 bar, whenthe inner pressure controlling means is spatially connected to the innerzone through at least one means selected from the group consisting of agas outlet means, a silicon seed crystals inlet means and an inner zoneconnecting means, which are spatially connected to an upper part of theinner zone instead of the silicon particle bed.
 10. The method accordingto claim 1, wherein a pressure controlling condition of thepressure-difference controlling means comprised in the inner pressurecontrolling means and/or the outer pressure controlling means isdetermined based on gas analysis of the gas that is present within ordischarged out of the inner zone and/or the outer zone by using a gasanalyzing means.
 11. The method of claim 1, wherein a packed bed ofpacking materials, which are not fluidized by the flow of the fluidizinggas, is formed in a lower part of the silicon particle bed with theheight of the packed bed being positioned below the outlet of thereaction gas inlet means through which the reaction gas is introducedinto the silicon particle bed.
 12. The method according to claim 8,wherein a pressure controlling condition of the pressure-differencecontrolling means comprised in the inner pressure controlling meansand/or the outer pressure controlling means is determined based on gasanalysis of the gas that is present within or discharged out of theinner zone and/or the outer zone by using a gas analyzing means.
 13. Themethod according to claim 9, wherein a pressure controlling condition ofthe pressure-difference controlling means comprised in the innerpressure controlling means and/or the outer pressure controlling meansis determined based on gas analysis of the gas that is present within ordischarged out of the inner zone and/or the outer zone by using a gasanalyzing means.